Multiple port catalytic combustion device and method of operating same

ABSTRACT

A catalytic combustor contains multiple sections for catalytically combusting an anode effluent. The anode effluent is divided into a plurality of portions with each portion routed to a different section or stage of the combustor. The proportioning of the anode effluent allows the combustor to be operated so that the flows combusted do not autoignite and various heat loads placed on the different stages of the combustor can be met. Additionally, the proportioning of the anode effluent allows the temperature within the various components of the combustor to be controlled so that a useful life of the combustor can be increased.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/213,641 filed on Aug. 7, 2002 now U.S. Pat. No. 6,712,603. Thedisclosure of the above application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to catalytic combustion devices, and morespecifically, to catalytic combustion devices that combust an anodeeffluent containing unused hydrogen (H₂) and a cathode effluentcontaining an unused oxidant, such as oxygen (O₂) or air, to produceheat.

BACKGROUND OF THE INVENTION

Catalytic combustion devices are employed in a variety of applications.A typical application involves the use of the catalytic combustiondevice to combust left over fuels that are contained within effluentsexhausted from a power system within which the catalytic combustiondevice is employed. The power systems within which the present inventioncan be employed use a fuel source, such as hydrogen (H₂) and an oxidantsource, such as oxygen (O₂) and/or air (O₂ admixed with nitrogen (N₂))to produce electrical power. The creation of electrical power within thepower system results in effluents that are exhausted from the powersystem. The effluents typically contain unused fuel in the form of H₂and unused oxidant in the form of O₂ and/or air. These effluentsrepresent a source of energy that can be used. To extract the energyfrom the effluents, these power systems typically employ a catalyticcombustion device that combusts the unused H₂ contained within theeffluent to produce heat that can be used within the power system tomeet a heat demand.

The amount of H₂ contained within the effluent will vary depending uponthe efficiency of the power system and the conditions under which thepower system is operated. Because the amount of H₂ contained within theeffluent varies, the catalytic combustion device typically includes aliquid fuel supply that can be used to increase the amount ofcombustible fuel within the combustion device so that heat demandsplaced on the combustion device by the power system can be met.Additionally, because the amount of H₂ contained within the effluentvaries, the amount of reaction occurring in any particular area withinthe combustion device can also vary and result in hot spots or locationsof excessive heat that can damage the combustion device. The effluentsand any liquid fuel flowing into the combustion device are a flammablefuel mixture. The temperature at which the fuel mixture will autoignitewill vary depending upon the composition of the fuel mixture.

Conventional combustion devices are designed to preclude autoignition ofthe fuel mixture. When autoignition of the fuel mixture within someareas occurs, the combustion device typically is damaged and possiblycompletely destroyed. In one solution to the autoignition concern, thefuel mixture is passed through a high density foam structure, prior toentering the area of the combustion device where the catalytic reactionis occurring and excessive heat build up can occur. The high densityfoam structure induces mixing as well as producing a high velocity exitgas. As long as the velocity of the combustible fuel mixture exiting thehigh density foam structure is greater than the fuel mixture flame speedand the material is below the autoignition temperature, the fuel mixtureupstream of the high density foam structure will not ignite. That is,the high density foam structure acts as a flame arrestor and preventsflame propagation across the high density foam structure.

While the use of the high density foam structure may prevent flamepropagation to an undesirable area in the combustion device, the highdensity foam structure produces a significant pressure drop as the fuelmixture flows through the high density foam structure. The pressure dropis undesirable because it may require the effluents flowing into thecombustion device to pass through additional equipment to increase thepressure of the effluents prior to entering the combustion device sothat adequate pressure and flow of the effluents through the combustiondevice is achieved. The extra equipment to pressurize the fuel flowincreases the complexity and cost of the system within which thecombustion device is employed.

Therefore, it would be desirable to provide a combustion device thatdoes not require the use of a flame arrestor or reduces the density ofthe flame arrestor so that the pressure drop across the flame arrestoris smaller and does not require the effluents to flow through anyadditional equipment prior to entering the combustion device.Additionally, it would be desirable to provide a combustion device thatcan utilize a liquid fuel injection system to provide a fuel to thecombustion device so that the combustion device can meet a heat demandof the power system during the start up operation of the power systemwhere the amount of effluent being exhausted by the power system may notbe sufficient to meet the heat demand of the power system.

SUMMARY OF THE INVENTION

The present invention is directed to a catalytic combustion device thatdiminishes and/or eliminates the need for a flame arrestor within thecombustion device. This is accomplished by splitting the H₂ containingeffluent exhausted by the power system into a plurality of flows andinjecting the plurality of flows in multiple locations along thecombustion device. The injection of the flows are controlled so that thefuel mixture within the combustion device is at a concentration that hasan autoignition temperature that is above the operating temperature ofthe various sections of the combustion device. The present inventionalso provides a method of operating such a combustion device. Theinvention further discloses a method of starting up the combustiondevice when the flow of H₂ within the anode effluent is not sufficientto meet the heat demand placed on the combustion device.

The catalytic combustion device of the present invention comprises afirst section that receives an oxidant feed stream and a first portionof an anode effluent stream. The oxidant feed stream and the firstportion of the anode effluent stream mix together in the first sectionto form a first stage flow stream. There is a second section downstreamfrom the first section. The second section has a first catalyst bed. Thesecond section receives the first stage flow stream from the firstsection and directs the first stage flow stream through the firstcatalyst bed. There is a third section downstream from the secondsection. The third section receives the first stage flow stream from thesecond section. The third section also receives a second portion of theanode effluent stream. The first stage flow stream mixes with the secondportion of the anode effluent stream in the third section to form asecond stage flow stream. There is a fourth section downstream from thethird section. The fourth section has a second catalyst bed. The fourthsection receives the second stage flow stream from the third section anddirects the second stage flow stream through the second catalyst bed.

The present invention discloses a method of operating a catalyticcombustor that combusts a flow of an anode effluent. The method includesthe steps of: 1) proportioning an anode effluent flow into a pluralityof portions; 2) supplying a first portion of the anode effluent flow toa first stage of the combustor; 3) supplying an oxidant feed stream tothe first stage of the combustor; 4) mixing the first portion of theanode effluent flow and the oxidant feed stream in the first stage ofthe combustor to form a first stage flow; 5) reacting the first stageflow within a first catalyst bed as the first stage flow passes throughthe first catalyst bed; 6) passing the first stage flow to a secondstage of the combustor that is downstream of the first stage; 7)supplying a second portion of the anode flow to the second stage of thecombustor; 8) mixing the second portion of the anode flow with the firststage flow within the second stage of the combustor to form a secondstage flow; and 9) reacting the second stage flow within a secondcatalyst bed as the second stage flow passes through the second catalystbed.

The present invention also discloses a method of starting a catalyticprocess within a catalytic combustor with a liquid fuel until asufficient flow of anode effluent is available. The method includes thesteps of: 1) supplying a liquid fuel flow to the combustor in a quantitysufficient to meet a heat demand of a known magnitude placed on thecombustor; 2) supplying an oxidant feed stream to the combustor; 3)mixing the liquid fuel and oxidant feed stream together in the combustorto form a fuel/oxidant flow; 4) vaporizing the fuel/oxidant flow with aheating element within the combustor as the fuel/oxidant flow passestherethrough; 5) reacting the vaporized fuel/oxidant flow in a primarycatalyst as the vaporized fuel/oxidant flow passes through the primarycatalyst so that the combustor generates heat to meet the heat demand;6) exhausting the reacted fuel/oxidant flow from the combustor; and 7)maintaining the supplying of the liquid fuel flow to the combustor untilthe combustor is supplied with an anode effluent flow of a magnitudecapable of allowing the combustor to meet the heat demand without theliquid fuel flow.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiments of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a combustor according to a firstpreferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of a different combustor according to asecond preferred embodiment of the present invention;

FIG. 3 is a close up cross-sectional view of a passageway of thecombustor of FIG. 1 taken along line 3—3;

FIG. 4 is a partial cross-sectional view of the combustor of FIG. 2taken along line 4—4 showing the use of a distribution rack to inject ananode effluent into the combustor; and

FIG. 5 is a schematic representation of a typical system in which thecombustor of the present invention can be employed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Shown in FIG. 1 is a combustor 20 in accordance with the principles ofthe present invention can catalytically combust liquid fuel 21, anodeeffluent 22, or liquid fuel 21 in combination with anode effluent 22.The combustor 20 is designed to combust liquid fuel 21 and/or anodeeffluent 22 catalytically with an oxidant, such as cathode effluent 24and/or air 25 while maintaining a controlled combustion process. Bycontrolling the combustion process, the temperature throughout thecombustor 20 can be controlled, different heat loads placed on thecombustor 20 can be met, and flammable or thermal combustion can beminimized and/or prevented, as will be described below. To accomplishthis, the combustor 20 is divided into a plurality of stages in whichcatalytic combustion occurs. Each stage receives a different fuel flowso that the catalytic combustion within each stage can be controlled,different heat loads placed upon the different stages of the combustorcan be met, and flammable combustion within each of the stages can beminimized and/or prevented.

The source of the fuels that the combustor 20 combusts depends upon thesystem within which the combustor 20 is employed. For example, as can beseen in FIG. 5, the combustor 20 can be employed as part of a fuel cellsystem 26. The fuel cell system 26 shown in FIG. 5 is a generic fuelcell system whose operation, for exemplary purposes, will now bediscussed.

In fuel cell system 26, a hydrocarbon fuel is processed in a fuelprocessor 28, for example, by reformation and partial oxidationprocesses, to produce a reformate gas 30 which has a relatively highhydrogen content on a volume or molar basis. Therefore, reference ismade to hydrogen-containing or relatively high hydrogen content. Thehydrogen-containing reformate can be made from a variety of sources,including hydrocarbon fuels such as methanol, ethanol, gasoline,alkaline, or other aliphatic or aromatic hydrocarbons.

As shown in FIG. 5, the fuel cell system 26 includes a fuel processor 28for catalytically reacting a reformable hydrocarbon fuel stream 32 and awater stream 34 in the form of steam. In some fuel processors, air isalso used in a combination partial oxidation/steam reforming reaction.In this example, fuel processor 28 also receives an air stream 36. Thefuel processor 28 contains one or more reactors wherein the reformablehydrocarbon fuel in stream 32 undergoes dissociation in the presence ofsteam from stream 34 and air from stream 36 to produce thehydrogen-containing reformate which is exhausted from the fuel processor28 as reformate stream 30. The fuel processor 28 typically also includesone or more downstream reactors, such as a water gas shift and/orpreferential oxidizer reactors which are used to reduce the levels ofcarbon monoxide in the reformate stream 30 to acceptable levels, forexample, below 20 ppm. The hydrogen-containing reformate stream 30 isfed through an anode chamber of a fuel cell stack 37. At the same time,oxygen in the form of air stream 38 is fed into a cathode chamber of thefuel cell stack 37. The hydrogen from the reformate stream 30 and theoxygen from the air stream 38 react in the fuel cell stack 37 to produceelectricity.

Anode effluent is exhausted from the anode side of the fuel cell stack37 in the form of anode effluent stream 39 which typically containsunreacted hydrogen. Cathode effluent is exhausted from the cathode sideof the fuel cell stack 37 in the form of cathode effluent stream 40which may contain unreacted oxygen. These unreacted gases representadditional energy which can be recovered in the form of thermal energyfor various heat requirements within the fuel cell system 26. The anodeeffluent 39 can be combusted catalytically in the combustor 20 withoxygen provided to the combustor 20 from air in stream 41 and/or thecathode effluent stream 40 depending on system operating conditions. Thecombustor 20 discharges an exhaust stream 42 to the environment and theheat 43 generated thereby may be directed to the fuel processor 28 orother components of the fuel cell system 26, as needed.

While FIG. 5 shows the combustor 20 being used as part of a fuel cellsystem 26, it should be understood that the combustor 20, according tothe principles of the present invention, is not limited to use solely ina fuel cell system 26. The combustor 20 of the present invention can beused in other fuel reforming systems that produce a hydrogen feed streamand have a given heat requirement. The combustor 20 mixes the anodeeffluent 39 with an oxidant, such as a cathode effluent 40 or air instream 41 and is catalytically combusted to produce heat. For example,the combustor 20 according to the principles of the present inventioncan be used with an adsorption exhaust and/or liquid fuel, a membraneexhaust and/or liquid fuel, or other sources of unused hydrogen, as willbe apparent to those skilled in the art.

The combustor 20, according to the principles of the present invention,is divided into a plurality of stages in which catalytic combustionoccurs. For example, as shown in FIG. 1, the combustor 20 is dividedinto first and second stages 44, 45. The first stage 44 of the combustor20 is upstream of the second stage 45. The anode effluent 22 thatsupplies unreacted H₂ to the combustor 20 is divided into a plurality ofanode effluent flows 46, 47. There is an anode effluent flow for eachstage of the combustor 20. For example, as shown in FIG. 1, the anodeeffluent 22 is separated into a first portion 46 and a second portion47. The anode effluent 22 is separated into the plurality of anodeeffluent flows depending upon the operation of combustor 20, as will bedescribed in more detail below. While the combustor 20 is shown anddiscussed as being divided into first and second stages 44, 45, itshould be understood that the combustor 20 can be divided into more thantwo stages that each contain a catalyst and each receive one of theplurality of anode effluent flows depending upon the application inwhich the combustor 20 is employed. Therefore, it should be understoodthat the combustor 20 according to the principles of the presentinvention, is not limited solely to first and second stages 44, 45.

Referring now to FIGS. 1 and 2, the combustor 20 has a chamber 48 forreceiving liquid fuel 21. A fuel injector 50 meters the liquid fuel 21so that a known quantity of liquid fuel 21 is supplied to the chamber48. An oxidant flow 52 is also supplied to chamber 48 to mix with theliquid fuel 21. The oxidant flow can be in the form of air flow 25and/or cathode effluent 24 as shown in FIG. 1. The term oxidant feedstream is used herein to generally describe the oxygen feed supplied tothe combustor 20 and encompasses cathode effluent 24, air flow 25 or anycombination thereof. For simplicity in explaining the operation of thecombustor 20, the oxidant flow will be referred to as air flow 25hereinafter, however, it should be understood that the oxidant flow 52can be formed from air flow 25, cathode effluent 24 or a combinationthereof regardless of the use of the term air flow 25 to describeoxidant flow 52. The liquid fuel 21 exits the fuel injector 50 in anonion-shaped flow pattern that is then pulled apart by air flow 25delivered via port 54 into chamber 48. The air flow 25 delivered viaport 54 is split into two stages. The first stage of air flow 25 isinjected tangentially in region 56 in order to induce high shear tobreak up the onion-shaped liquid fuel 21 into a fine mist of particlesin chamber 48. The second stage of the air flow 25 supplied from port 54is radially injected into chamber 48 through gap 58. Alternatively, thesecond stage of the air flow 25 could be radially injected throughorifices (not shown) spaced around the circumference of chamber 48rather than through the gap 58. Optionally, as was stated above, the airflow 25 supplied to chamber 48 via port 54 can be supplied partially orentirely from the cathode effluent 24 via line 60. In this case, controlvalves 62 are positioned on line 60 to control the fluid that issupplied to chamber 48 via port 54.

The combustor 20 has a generally cylindrical shell 66 with an inlet 68and an outlet 70. The inlet 68 of the combustor 20 leads to a primarymixing chamber 72. The primary mixing chamber 72 receives the liquidfuel/air mixture 64 from chamber 48. The primary mixing chamber 72 alsoreceives a first portion 46 of the anode effluent 22 and the cathodeeffluent 24. The first portion 46 flows into an annular chamber 74 viaport 76. The cathode effluent 24 also flows into the annular chamber 74via port 76 in the configuration shown in FIG. 2 or via port 78 in theconfiguration shown in FIG. 1. The first portion 46 and the cathodeeffluent 24 mix together in the annular chamber 74 and flow into theprimary mixing chamber 72 via passageway 80, as shown in FIG. 3. Theliquid fuel/air mixture 64, the first portion 46 and the cathodeeffluent 24 mix together in the primary mixing chamber 72 to form afirst stage flow stream 82.

The first stage flow stream 82 then flows through a distribution media84 that is a porous bed which provides a tortuous path therethrough topromote turbulent flow and intimate mixing of the various components ofthe first stage flow stream 82 before exiting the distribution media 84.Preferably, the first stage flow steam 82 exits the distribution media84 as a homogeneous flow. Preferably, the distribution media 84 is a 40ppi (pore per linear inch) reticulated foam structure made of YZA(Yttria-Zirconia-Aluminia), although the distribution media 84 couldalso be made from many alternate materials, such as, silicon carbide orzironia-toughened aluminia, or alternate structures, such as, a wovenmetal matrix, parallel channel monolith, sintered metal series ofscreens, etc. depending upon the mixing and distribution requirements,as will be apparent to those skilled in the art.

The first stage flow stream 82 then passes through a heating element 86.As presently preferred, the heating element 86 is an electrically heatedstructure 86 that supplies heat to vaporize any liquids, such as theliquid fuel 21, within the first stage flow stream 82. Optionally, butpreferably, the electrically heated structure 86 also contains acatalyst and is an electrically heated catalyst 88. Preferably, theelectrically heated catalyst 88 is a metal honeycomb structure withdensity of about 350 cpsi (cells per square inch) with a palladiumcatalyst, although other precious metals are possible, as will beapparent to those skilled in the art. The electrically heated catalyst88 along with vaporizing the liquids initiates the catalytic reaction ofthe first stage flow stream 82. The amount of heat produced by theelectrically heated catalyst 88 is adjustable and can be varieddepending upon the needs of the combustor 20 and the system within whichthe combustor 20 is employed, as will be discussed in more detail below.

The first stage flow stream 82 then flows through an optional, butpreferred, light-off catalyst 90. Preferably, the light-off catalyst 90is a 40 ppi reticulated foam that uses a platinum/palladium catalyst,although alternate precious metals or combinations of such are possibledepending on the application requirements and the economic tradeoff atthe time of inception, as will be apparent to those skilled in the art.Alternate geometry foams or structures are also possible, such asdescribed above in relation to the distribution media 84, with thedesire to induce turbulence and improve reaction stability.

The first stage flow stream 82 then passes through a first main catalyst92. The first main catalyst 92 is preferably a 600 cpsi parallel channelmonolith made of cordiorite with similar catalyst as described for thelight-off catalyst 90. The first main catalyst 92 can also be made ofalternate materials or geometric configurations, such as described withrelation to the light-off catalyst 90. The first stage flow stream 82reacts within the first main catalyst 92 to combust the hydrogen withinthe first stage flow stream 82 and produces heat.

The first stage flow stream 82 then passes through an uncatalyzedradiant shield 94. Preferably, the radiant shield 94 is a 400 cpsiparallel channel uncatalyzed cordiorite monolith or a reticulated foamsimilar to the distribution media 84. The radiant shield 94 acts tominimize ignition of downstream flows (minimize conditions which allowhot spots within the catalysts) by preventing back flow of potentiallycombustible mixtures to the upstream main catalyst 92 which could act asan ignition source.

The first stage flow stream 82 then exits the first stage 44 of thecombustor 20 and either flows directly to the second stage 45 of thecombustor 20, as shown in FIG. 1, or alternatively, flows through a heatexchanger 96 and then into the second stage 45 of the combustor 20, asshown in FIG. 2. When the first stage flow stream 82 flows through aheat exchanger 96, the heat exchanger 96 extracts heat from the firststage flow stream 82 for use in meeting a heat demand of the system. Theheat demand placed upon the heat exchanger 96 will vary depending uponthe needs of the system.

The first stage flow stream 82 enters a second primary mixing chamber 98in the second stage 45 of the combustor 20. The second portion 47 of theanode effluent flow 22 also flows into the second primary mixing chamber98 to mix with the first stage flow stream 82. The second portion 47 canbe supplied to the second primary mixing chamber 98 in a variety ofways. For example, as can be seen in FIG. 1, the second portion 47 canflow into an annular chamber 100 via port 102 and then enter the secondprimary mixing chamber 98 via openings 104 located around the peripheryof the annular chamber 100. Preferably, the openings 104 are spacedabout the periphery of the annular chamber 100 to facilitate the mixingof the second portion 47 with the first stage flow stream 82 whenentering the second primary mixing chamber 98.

Alternatively, as can be seen in FIGS. 2 and 4, the second portion 47can flow into a manifold 106 in an injection rack 108. The injectionrack 108 is positioned within the second primary mixing chamber 98 andhas a plurality of generally parallel tubes 110 that extend across thesecond primary mixing chamber 98. Each tube 110 is in fluidcommunication with the manifold 106 and receives the second portion 47of anode effluent flow 22. Each tube 110 has a plurality of openings 112that are spaced along the tubes 110 and through which the second portion47 enters the second primary mixing chamber 98. Preferably, the openings112 are positioned on the tubes 110 so that the openings 112 on adjacenttubes 110 face one another and the second portion 47 forms a curtain orfilm of anode effluent that extends across the second primary mixingchamber 98. The first stage flow stream 82 then flows through thecurtain of second portion 47 of anode effluent flow 22 and mixestherewith in the second primary mixing chamber 98.

The mixing of the first stage flow stream 82 and the second portion 47in the second primary mixing chamber 98 forms a second stage flow stream114. The second stage flow stream 114 flows from the second primarymixing chamber 98 through a second distribution media 116. The seconddistribution media 116 is the same as the distribution media 84 in thefirst stage 44 of the combustor 20, with the exception of its size,which may vary. That is, the size of the second distribution media 116may vary depending upon the amount of mixing of the second stage flowstream 114 required in the second distribution media 116. Preferably,the second stage flow stream 114 exits the second distribution media 116as a generally homogeneous stream.

The second stage flow stream 114 then passes through a second primarycatalyst 118. The second primary catalyst 118 is preferably a 600 cpsiparallel channel monolith made of cordiorite with a similar catalyst asdescribed for the first main catalyst 92 and the light-off catalyst 90.The second stage flow stream 114 reacts within the second primarycatalyst 118 to combust the hydrogen within the second stage flow stream114 and produce heat.

The second stage flow stream 114 exits the second primary catalyst 118and flows through outlet 70 and through heat exchanger 120 that is usedto extract heat from the second stage flow stream 114 to meet a heatdemand of the system within which the combustor 20 is employed. Thesecond stage flow stream 114 is then exhausted to the environment. Theexhausted second stage flow stream 114 preferably contains little or nounused hydrogen.

The operation of the combustor 20 will now be described. During astart-up of the system within which the combustor 20 is employed, thesystem may or may not be producing anode effluent 22 and, if available,may contain little or no hydrogen to be catalytically combusted withinthe combustor 20 to meet a heat demand placed on the combustor 20 by thesystem. Therefore, during start-up the combustor 20, depending upon theavailability of anode effluent 22 and the amount of hydrogen containedtherein, may exclusively or supplementally use liquid fuel 21 to providea start-up fuel so that the combustor 20 can generate heat and meet aheat demand placed on the combustor 20.

Liquid fuel 21 is metered into chamber 48 via the fuel injector 50 andair flow 25 is supplied to chamber 48 via port 54. Preferably, duringthe start-up all the air flow 25 is supplied to the inlet mixing chamber48 via port 54. The liquid fuel/air mixture 64 then flows into theprimary mixing chamber 72 wherein a first portion 46 of anode effluent22 and/or cathode effluent 24 can also be mixed with the liquid fuel/airmixture 64. However, as stated above, during the start-up of the systemand of the combustor 20, little or no anode and cathode effluents 22, 24are expected to be available. The liquid fuel/air mixture 64 and anyanode and/or cathode effluents 22, 24 supplied to the primary mixingchamber 72 mix together and form the first stage flow stream 82. Thefirst stage flow stream 82 then flows through the distribution media 84where it is thoroughly mixed and preferably emerges as a generallyhomogeneous flow.

The first stage flow stream 82 then enters into the electrically heatedcatalyst 88. The electrically heated catalyst 88 is heated viaelectricity to a temperature that vaporizes the first stage flow stream82 so that no liquid fuel exits the electrically heated catalyst 88.Additionally, the electrically heated catalyst 88 also initiates thecatalytic reaction of the first stage flow stream 82. The first stageflow stream 82 then passes through the light-off catalyst 90, the firstmain catalyst 92, the radiant shield 94 and on to the second primarymixing chamber 98 in the second stage 45 of the combustor 20 eitherdirectly or through the optional heat exchanger 96. Upon entering thesecond primary mixing chamber 98, the first stage flow stream 82 willmix with the second portion 47 of anode effluent 22, although little orno anode effluent is expected to be available, to form a second stageflow stream 114. The second stage flow stream 114 is then mixed withinthe second distribution media 116 and flows through the second primarycatalyst 118 through the heat exchanger 120 and then exhausted to theenvironment.

During the start-up of the combustor 20, the first stage flow stream 82catalytically combusting in the electrically heated catalyst 88, thelight-off catalyst 90 and the first main catalyst 92 will produce heatthat will transfer throughout the combustor 20 and increase thetemperature throughout the combustor 20. As a result, the temperaturewithin the primary mixing chamber 72 and the distribution media 84 willincrease. Eventually, the temperature within the distribution media 84will reach a temperature sufficient for the liquid fuel 21 within thefirst stage flow stream 82 to vaporize as the first stage flow stream 82passes through distribution media 84 such that the electrically heatedcatalyst 88 will no longer need to be heated to cause the liquid fuel 21to vaporize. Preferably, the distribution media 84 has a thermocouple122 embedded within the distribution media 84 or, alternatively,positioned adjacent the distribution media 84 so that the temperature ofthe distribution media 84 is known during the operation of the combustor20. Based on the temperature of the distribution media 84, the electriccurrent flowing to the electrically heated catalyst 88 is adjusted asneeded to supply heat to vaporize the liquids within the first stageflow stream 82. Therefore, after operating the combustor 20 for asufficient length of time, the electrically heated catalyst 88 in mostconditions can be turned off and the back radiation and conduction fromthe heat of reaction of the first stage flow stream 82 in theelectrically heated catalyst 88, light-off catalyst 90 and the firstmain catalyst 92 will support liquid vaporization within thedistribution media 84. While the measuring of the temperature of thedistribution media 84 is discussed as being performed by the use of atemperature sensor 122, such as a thermocouple, it should be understoodthat a variety of means of measuring or predicting the temperaturewithin the distribution media 84, as will be apparent to those skilledin the art, can be employed without departing from the scope of theinvention as defined by the claims. It should also be understood thattemperatures at other locations within the first stage 44 of thecombustor 20 can be measured and used to control the operation of theelectrically heated catalyst 88, as will be apparent to those skilled inthe art, and still be within the scope of the invention as defined bythe claims.

As the amount of fuel (H₂) contained within the anode effluent 22increases, the combustor 20 can operate with decreasing amounts ofliquid fuel 21. As a result, the amount of liquid fuel 21 supplied tothe combustor 20 is decreased as the amount of hydrogen contained withinthe anode effluent 22 increases to the point where the need for liquidfuel 21 in the combustor 20 to meet the heat demands placed on thecombustor 20 is eliminated. When this state is reached, liquid fuel 21is no longer supplied to the combustor 20. However, it should beunderstood that there may be periods of operation of the combustor 20,such as when exceptionally high heat demands are placed upon thecombustor 20 or when the amount of H₂ within the anode effluent 22 isinsufficient. In such circumstances, it would be desirable to injectliquid fuel 21 into the combustor 20 to supplement the anode effluent 22and increase the amount of heat generated by the combustor 20.Accordingly, the combustor 20 is designed to run on the anode effluent22, the liquid fuel 21, and/or a mixture of the anode effluent 22 andthe liquid fuel 21 at any time. The combustor 20 is operated to consumea majority, and preferably substantially all, of the unused hydrogencontained within the anode effluent 22 so that no unused hydrogen isexhausted from the combustor 20. Therefore, it is preferred to minimizethe use of liquid fuel 21 so that most or all of the liquid fuel 21 andhydrogen in the anode effluent 22 is consumed in the combustor 20.

Preferably, the cathode effluent 24 supplied to the combustor 20 issufficient to oxidize all the hydrogen contained in the anode effluent22 and any liquid fuel 21 supplied to the combustor 20. However, thecombustor 20 can also be supplied with air flow 25 through the port 54,as was described above, to supplement the cathode effluent 24, toachieve complete combustion.

When the combustor 20 and the system within which the combustor 20 isemployed are fully operational, the combustor 20 consumes all of theanode effluent 24 and any liquid fuel 21 injected into the combustor 20using the cathode effluent 24 and/or air flow 25. The anode effluent 22is proportioned into a plurality of portions of anode effluent flowsdepending upon how the combustor 20 is to be operated. For example, itmay be desired to prevent the hydrogen concentration within the firststage flow stream 82 and/or the second stage flow stream 114 from havinga sufficient concentration of hydrogen that the temperature within therespective first and second stages 44, 45 of the combustor 20 causes thefirst and/or second stage flow streams 82, 114 to autoignite.Alternatively, it may be desired to operate the combustor 20 with aspecific temperature distribution or profile so that various heatdemands placed on the combustor 20 are met and/or distributed throughoutthe combustor 20.

To operate the combustor 20 so that autoignition of the first and/orsecond stage flow streams 82, 114 is minimized and/or prevented, one ormore temperature sensors 124, such as thermocouples, are positionedwithin the first stage 44 of the combustor 20 so that the temperaturewithin the first stage 44 is known. The temperature at which the firststage flow stream 82 will autoignite depends upon the operatingconditions of the combustor 20 and the amount of hydrogen containedwithin the first stage flow stream 82, as will be apparent to thoseskilled in the art. The amount of anode effluent contained within thefirst portion 46 of anode effluent 22 is proportioned so that theconcentration of hydrogen within the first stage flow stream 82 is belowa concentration that will autoignite at the measured temperature of thefirst stage 44 of the combustor 20. For example, thermocouple 124 can bepositioned within the light-off catalyst 90. Based on the measuredtemperature, the amount of anode effluent 22 in the first portion 46will be controlled by valve 128 so that the hydrogen concentration isbelow the autoignition level at the measured temperature. The remaininganode effluent is proportioned to other stages of the combustor 20. Bypreventing the first stage flow stream 82 from autoigniting within thecombustor 20, damage to the components of the combustor can be avoided.Additionally, the distribution media 84 may not need to provide as muchor any flame suppression as is the case in conventional prior artcombustors. As a result, the distribution media 84 can be configured andadapted to provide a generally homogeneous first stage flow stream 82without the high pressure drop associated with a conventional designwhich require substantial flame arresting characteristics.

It is also desirable to prevent the second stage flow stream 114 fromautoigniting within the second stage 45 of the combustor 20. Therefore,like the first stage 44, the second stage 45 can also have one or moretemperature sensors 126, such as thermocouples, distributed throughoutthe second stage 45 of the combustor 20 so that the temperature withinthe second stage 45 is known. The amount of anode effluent containedwithin the second portion 47 of anode effluent flow 22 is proportionedto prevent autoignition of the second stage flow stream 114. Forexample, thermocouple 126 can be placed in the second primary catalyst118 and the amount of anode effluent 22 proportioned to the secondportion 47 adjusted based on the measured temperature. The proportioningof the anode effluent flow 22 into the plurality of portions iscontrolled by control valve 128 that operates to divide the anodeeffluent 22 into appropriate amount of first and second portions 46, 47.Depending upon the design of the combustor 20 and the number of stagestherein, multiple control valves 128 may be employed to proportion theanode effluent 22. The number of stages will depend on concentrations,and the means to extract heat from the stream inbetween or withinstages.

Instead of using control valve 128 to proportion the anode effluent, oneor more orifice plates (not shown) can be used. The orifice plates areselected so that a desired ratio or proportioning of the anode effluent22 is achieved. However, static orifice plates will not allow dynamiccontrol of the proportioning of the anode effluent 22 and, as such, theuse of control valve 128 is presently preferred. Additionally, it shouldbe understood that other means of proportioning the anode effluent 22,as will be apparent to those skilled in the art, can be employed andstill be within the scope of the invention as defined by the claims.

Because the proportioning of the first and second stage flow stream 82,114 can vary and the temperatures within the first and second stages 44,45 the combustor 20 can also vary, the radiant shield 94 in the firststage 44 preferably minimizes conditions which allow for hot spotswithin the first main catalyst 92 to cause ignition of the second stageflow stream 114. The radiant shield 94 functions by preventing back flowof the second stage flow stream 114 into the upstream first maincatalyst 92, which could act as an ignition source. Preferably, theoperation of the first stage 44 of the combustor 20 is controlled sothat the temperature of the first stage flow stream 82 entering thesecond primary mixing chamber 98 is below the autoignition temperatureof the second portion 47 of anode effluent 22 so as to minimizeautoignition and hot spots within downstream stage(s).

The temperature of the first stage flow stream 82 entering the secondprimary mixing chamber 98 can be controlled in a number of ways. Forexample, the amount of anode effluent 22 contained within the firstportion 46 can be controlled based upon the temperature of the firststage flow stream 82 exiting the first main catalyst 92. Preferably, asshown in FIG. 2, the first stage flow stream 82 can go through heatexchanger 96 prior to entering the second primary mixture chamber 98.The heat exchanger 96 extracts heat from the first stage flow stream 82so that the temperature of the first stage flow stream 82 entering thesecond primary mixing chamber 98 is below the autoignition temperatureof the second portion 47 of anode effluent 22.

The combustor 20, as was mentioned above, can be operated so thatvarious heat demands placed upon the combustor 20 are met. The anodeeffluent 22 is proportioned so that the various heat exchangers thatextract heat from the combustor 20 can each meet the heat demand placedupon the heat exchangers. For example, as shown in FIG. 2, the amount ofanode effluent 22 that is proportioned to the first stage 44 can beadjusted so that the temperature of the first stage flow stream 82flowing through the heat exchanger 96 is sufficient to meet the heatdemand placed upon the heat exchanger 96. Liquid fuel 21 can also besupplied to the first stage 44 to meet the heat demand placed on heatexchanger 96. The amount of anode effluent 22 that is proportioned tothe second stage 45 can also be adjusted so that the temperature of thesecond stage flow stream 114 flowing through the second heat exchanger120 is sufficient to meet the heat demand placed upon the second heatexchanger 120. In this manner, the combustor 20 can be operated to meetthe various heat demands placed upon the combustor 20.

As stated above, liquid fuel 21 can be injected into the first stage 44of the combustor 20 to supplement the amount of hydrogen containedwithin the first stage flow stream 82 so that the combustor 20 can meetthe various heat demands. For example, when the heat demand placed uponthe first heat exchanger 96 is greater than the amount of heat that canbe generated by routing all of the anode effluent 22 to the first stage44 of the combustor 20, liquid fuel 21 can be injected into the firststage 44 of the combustor 20 to meet the heat demand placed upon thefirst heat exchanger 96. Similarly, if the heat demand placed upon thesecond heat exchanger 120 requires that all of the anode effluent 22 beproportioned to the second stage 45, liquid fuel 21 can be injected intothe first stage 44 so that the first stage flow stream 82 can generatesufficient heat to meet the heat demands placed upon the first heatexchanger 96.

While the combustor 20 has been shown as having two stages 44, 45 andtwo heat exchangers 96, 120 associated with the respective first andsecond stages 44, 45, it should be understood that the combustor 20 canhave more than two stages and can also have more than two heatexchangers and still be within the scope of the invention as defined bythe claims. Furthermore, it should be understood that there can be morethan one heat exchanger for each stage of the combustor 20, as will beapparent to those skilled in the art, and still be within the scope ofthe invention as defined by the claims.

Preferably, the combustor 20 is designed so that the first and secondstages 44, 45 can be operated to simultaneously meet the various heatdemands placed upon the combustor 20 and avoid autoignition of the firstand second flow streams 82, 114 within the combustor 20. That is, thecombustor 20 can preferably meet the heat demands placed upon thecombustor 20 without autoignition occurring within the combustor 20.

The above-described combustor 20 and operation of the same enablesexcess fuel contained within an anode effluent 22 to be catalyticallycombusted within the combustor 20 to provide useful energy. Thecombustor 20 can be controlled so that no fuel streams within thecombustor 20 autoignite and no flammable combustion occurs.Additionally, the combustor 20 can be operated so that no hot spotsoccur in any of the catalysts within the combustor 20 so that the lifespan of the combustor and the catalysts can be increased. Because thecombustor 20 can be operated so that the flows within the combustor 20do not autoignite, flame suppressors, if any, within the combustor 20 donot need to be as substantial as in conventional combustors and, as aresult, a pressure drop across the flame suppressors will be reduced andresult in a more efficient combustor 20. Additionally, the combustor 20can be operated so that heat demands placed upon different stages of thecombustor 20 can be met.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method of starting a catalytic process within a tailgas combustorwith a liquid fuel until a sufficient flow of an anode effluent isavailable, the method comprising the steps of: supplying a liquid fuelflow to the combustor in a quantity sufficient to meet a heat demand ofa known magnitude placed on the combustor; supplying an oxidant feedstream to the combustor; mixing said liquid fuel and oxidant feed streamtogether in the combustor to form a fuel/oxidant flow; vaporizing saidfuel/oxidant flow with a heating element within the combustor as saidfuel/oxidant flow passes therethrough; reacting said vaporizedfuel/oxidant flow in a primary catalyst as said vaporized fuel/oxidantflow passes through said primary catalyst so that the combustorgenerates heat to meet said heat demand; exhausting said reactedfuel/oxidant flow from the combustor and maintaining the supplying ofsaid liquid fuel flow to the combustor until the combustor is suppliedwith an anode effluent flow of a magnitude capable of allowing thecombustor to meet said heat demand without said liquid fuel flow.
 2. Themethod of claim 1, wherein said step of mixing includes passing saidliquid fuel flow and said oxidant feed stream through a distributionstructure that mixes said liquid fuel flow and oxidant feed streamtogether to form said fuel/oxidant flow as said liquid fuel flow andoxidant feed stream pass through said distribution structure.
 3. Themethod of claim 2, further including the steps of: monitoring atemperature of said distribution structure to determine when saiddistribution structure has a temperature that is capable of vaporizingsaid liquid fuel flow passing through said distribution structure;vaporizing said liquid fuel flow in said distribution structure as saidliquid fuel flow passes through said distribution structure; anddisabling said heating element when said distribution structure iscapable of vaporizing said liquid fuel flow passing through saiddistribution structure.
 4. The method of claim 2, wherein the step ofmixing includes mixing said liquid fuel flow and oxidant feed streamtogether in said distribution structure to form a generally homogenousfuel/oxidant flow.
 5. The method of claim 1, wherein said heatingelement is an electrically heated catalyst and the method furtherincludes the step of initiating a catalytic reaction of saidfuel/oxidant flow with said electrically heated catalyst as saidfuel/oxidant flow passes through said electrically heated catalyst. 6.The method of claim 1, further including the step of passing saidfuel/oxidant flow through a light-off catalyst prior to said primarycatalyst.
 7. The method of claim 1, further including the steps of:monitoring a parameter of the combustor indicative of said heat demandof a known magnitude; and adjusting said liquid fuel flow supplied tothe combustor based upon said parameter.
 8. The method of claim 1,further including the steps of: determining a quantity of anode effluentflow being supplied to the combustor; and adjusting said liquid fuelflow supplied to the combustor based upon said determined quantity ofanode effluent flow and said heat demand.
 9. A method at operating acatalytic tailgas combustor to combust a flow of an anode effluent, themethod comprising the steps of: proportioning an anode effluent flowinto a plurality of portions; supplying a first portion of said anodeeffluent flow to a first stage of the combustor; supplying an oxidantfeed stream to said first stage of the combustor; mixing said firstportion of said anode effluent flow and said oxidant feed stream in saidfirst stage of the combustor to form a first stage flow; reacting saidfirst stage flow within a first primary catalyst as said first stageflow passes through said first primary catalyst; passing said firststage flow to a second stage of the combustor downstream of said firststage; supplying a second portion of said anode flow to said secondstage of the combustor; mixing said second portion of said anode flowwith said first stage flow within said second stage of the combustor toform a second stage flow; and reacting said second stage flow within asecond primary catalyst as said second stage flow passes through saidsecond primary catalyst.
 10. The method of claim 9, wherein said step ofproportioning said anode effluent flow includes the step ofproportioning said anode effluent flow between said plurality ofportions so that said first stage flow formed in said first stage of thecombustor has a composition that will not autoignite within said firststage of the combustor.
 11. The method of claim 10, further includingthe step of: measuring a temperature of said first stage of thecombustor; and wherein: said step of proportioning said anode effluentflow includes proportioning said anode effluent flow between saidplurality of portions based upon said measured temperature of said firststage.
 12. The method of claim 10, wherein said step of proportioningsaid anode effluent flow between said plurality of portions includesproportioning said anode effluent flow between said plurality ofportions so that a stage flow formed in any stage of the combustor has acomposition that will not autoignite within said any stage of thecombustor.
 13. The method of claim 12, further including the step ofmeasuring a temperature of each stage of the combustor, and wherein saidstep of proportioning said anode effluent flow includes proportioningsaid anode effluent flow between said plurality of portions based upon ameasured temperature of an immediately preceding stage upstream fromsaid any stage of the combustor so that a stage flow formed in said anystage of the combustor has a composition that will not autoignite withinsaid any stage of the combustor.
 14. The method of claim 9, wherein saidstep of proportioning said anode effluent flow includes the step ofproportioning said anode effluent flow between said plurality ofportions so that a stage flow formed in any stage of the combustor has acomposition that will generate a sufficient amount of heat when reactedwithin said any stage to meet a heat demand of a known magnitude imposedon said any stage.
 15. The method of claim 14, further including thestep of routing a stage flow from at least one stage of the combustorthrough a heat exchanger to extract heat from said stage flow.
 16. Themethod of claim 9, wherein said step of supplying said second portionincludes injecting said second portion into said second stage throughopenings in a periphery of an interior of said second stage.
 17. Themethod of claim 9, wherein said step of supplying said second portionincludes the step of injecting said second portion into said secondstage through a plurality of generally parallel members that extendacross said second stage.
 18. The method of claim 17, wherein said stepof injecting said second portion includes injecting said second portioninto said second stage through opposed openings on adjacent members. 19.The method of claim 9, wherein said step of proportioning said anodeeffluent flow includes the step of proportioning said anode effluentflow between said plurality of portions so that a temperature in anystage of the combustor does not exceed a predetermined magnitude forsaid any stage.
 20. The method of claim 19, further including the stepof measuring a temperature of each stage of the combustor, and whereinsaid step of proportioning of said anode effluent flow between saidplurality of portions is based upon said measured temperature of saideach stage of the combustor.